Field theory analysis of S=1 antiferromagnetic bond-alternating chains in the dimer phase

TL;DR

This paper uses field theory to analyze the low-energy excitations of S=1 antiferromagnetic bond-alternating chains near the dimer-Haldane phase transition, successfully explaining experimental neutron scattering data and predicting differences in Raman spectra.

Contribution

It develops a sine-Gordon field theoretical model for the system, providing new insights into its excitation spectrum near the critical point.

Findings

Good agreement with neutron scattering experiments

Prediction of absence of sharp peaks in Raman spectra

Field theory accurately describes low-energy excitations

Abstract

Dynamics of S=1 antiferromagnetic bond-alternating chains in the dimer phase, in the vicinity of the critical point with the Haldane phase, is studied by a field theoretical method. This model is considered to represent the compound Ni(C$_9$H$_{24}$N$_4$)(NO$_2$)ClO$_4$ (abbreviated as NTENP). We construct the sine-Gordon (SG) field theory as a low-energy effective model of this system, starting from a Tomonaga-Luttinger liquid at the critical point. Using the exact solution of the SG theory, we give a field theoretical picture of the low-energy excitation spectrum of NTENP. Results derived from our picture are in a good agreement with results of inelastic neutron scattering experiments on NTENP and numerical calculation of the dynamical structure factor. Furthermore, on the basis of the obtained theoretical picture, we predict that the sharp peaks correspond to a single elementary excitation are absent in the Raman scattering spectrum of NTENP in contrast to the inelastic neutron scattering spectrum.